1. Field of the Invention
The field of the present invention is vacuum boosters of a type for operating a master cylinder for a brake or a clutch in an automobile in a boosting manner by a vacuum pressure, and particularly, improvements of such vacuum boosters comprising a pedestal formed on a rear wall of a booster shell and comprised of a rectangular seating face wall surrounding an axis of the booster shell, and a peripheral wall inclined from the seating face wall, the pedestal being attached to a vehicle body through four connecting bolts fixedly mounted on the seat face wall in proximity to four corners thereof.
2. Description of the Related Art
In such a conventional vacuum booster, the peripheral wall of the pedestal is formed bulged on the rear wall of the booster shell, so that the length from a general wall of the rear wall to the seating face wall is uniform at various portions (see for example, Japanese Utility Model Application Laid-open No. 79058/82).
In the conventional vacuum booster of the type above-described, during the boosting operation, stress tends to be concentrated around each of the corners of a peripheral edge of the pedestal due to an axial tensile load acting on the booster shell.